1. Field of the Invention
The present invention relates to imaging devices, and more particularly, to a media feed unit for an ink jet printer.
2. Description of the Related Art
A paper path in a typical ink jet printer includes a paper pick mechanism which transports a media sheet past an ink jet printhead and delivers the media sheet to a sheet exit system.
Ink jet printers have used many types of paper picking mechanisms. For example, many ink jet printers use D-rollers with a spring loaded pressure plate or a spring loaded pressure plate that is pushed in and out of engagement with a fixed back-up roller at the top of the paper stack. Downstream of the paper picking mechanism, many such systems use corner bucklers to separate the top sheet of paper from the rest of the stack. Further downstream of that separator mechanism is usually a precision feed roll and spring loaded pressure rolls that work in conjunction with the feed roll to create accurate paper feed motions of the correct increment. As print quality requirements are continuously increased, the need for higher precision feed rolls and associated gear train is increased.
Downstream of the feed rolls is the exit system, which typically includes a driven segmented exit roll which engages the non-printed side of the media sheet, and multiple sets of back-up rollers, typically star wheels, positioned opposite the exit roll segments. The function of the exit roll is to feed the paper out of the printer once it has left the feed roll nip. Since the ink is still wet, the star wheels are designed to have a small contact point on the printed side of the media sheet so that ink on the printed side of the media sheet is not smeared or removed as the sheet exits the printer.
The low end of the ink jet printer market includes printers that print with large ink drops that do not require the precision of ink drop placement that the smaller drops do. In turn, for the low end printer, the incremental movement of the media sheet does not require as great of precision. To remain price competitive, these printers need to be as small and low cost as possible while still maintaining a reasonable print quality. However, the feed roll with associated pressure rolls and springs, the exit roll system including exit roll segments and associated star wheels and pressure springs, and the gear train to move these rolls precisely, drive up the cost of the printers.
Accordingly, what is needed in the art is a low end printer that can operate with acceptable incremental sheet movement without many of the media transport components that are typically found on low end printers.
The present invention is directed to a printer that can operate with acceptable incremental sheet movement without many of the media transport components that are typically found on low end printers.
One aspect of the invention is a printer having a media path through which a media sheet having a first surface and a second surface is transported. The printer includes a printhead having an ink jetting nozzle plate defining a print zone. The printer further includes a media frame having a base and an extension portion angularly extending upwardly away from the base. The base has a first edge spaced apart from a second edge. The first and second edges are located for contacting the media sheet on the first surface. The extension portion has a support surface for providing support for the media sheet at the first surface. The printer further includes a roller assembly having a roller positioned opposed to the extension portion, the roller engaging the second surface of the media sheet to define a line of contact with the media sheet. The line of contact defined by the roller and the first edge of the base determine a first curvature of the media sheet having a first radius, and the first edge of the base and the second edge of the base determine a second curvature of the media sheet having a second radius.
In another aspect of the invention, the media frame is configured such that the media path has a downward trajectory. The roller of the roller assembly is positioned opposed to an extension plate, wherein the roller engages the second surface of the media sheet to transport the media sheet in the media path.
An advantage of the present invention is that a smaller and lower cost printer is possible without sacrificing reasonable print quality.
Another advantage is that the present invention provides a simplified media transport system, which eliminates the need for a mechanically complicated media transport system including feed rolls with associated pressure rolls and springs, exit rolls with associated star wheels and star wheels springs, and the gear train to move these rolls.